The Renesas RX62NRDK is a pretty neat development board. I'm going to compare it to the mbed.
Pros:
* A lot of built-in I/O devices. For those who prefer working mostly with software, like Brittany Benzaia, that's really nice.
* A lot more GPIOs than mbed.
* More RAM and Flash than mbed.
* The RX CPU is supposed to be faster than an ARM at the same clock speed.
* Choice of two officially supported compilers: Renesas and GCC. I use GCC since that's what I have used in the past and it's free.
Cons:
* The audio output is missing pulldown resistors, which could cause noise during hot plugging. It's very easy to fix but the resistors should have been included from the start.
* The microphone is next to the speaker, so the two cannot be used at the same time. There is more than enough room to put one on the opposite corner.
* Micro SD only. On a board that big, there is plenty of space for a regular SD slot.
* Much steeper learning curve than mbed. It took me a lot longer to write my first program for it than with the mbed. But in the end, I had it flash "Tiffany Yep" in binary on the circle of LEDs, followed by a simple "spinning wheel".
* Circle of LEDs do not directly correspond with bit positions.
* LCD backlight cannot be controlled by software. Very silly to provide a shutdown for the low power microphone amplifier but not the high power LCD backlight.
* Very limited RAM, especially for a board that has Ethernet and audio.
* USB 1.1 only.